| In this paper, the preparation process and properties of three-layer composite materials (4343A1/4A60A1/08A1 steel) were investigated. This composite material was mainly used in the core part of air cooling system in thermal power plant---Base material of air cooled fin. The base pipe material must contained the advantages of high temperature resistance, corrosion resistance, high strength, thermal conductivity, brazing property and so on.3003 aluminum heat radiating fins are welded on the base tube surface to form a heat radiating system unit. Due to the brazing, thermal conductivity, corrosion resistance and other properties of 4343 aluminum and aluminum 4A60 had good resistance to rot, plastic and thermal conductivity, and 08A1 steel had the advantages of high strength, easy processing, and low price, therefore,4343 aluminum/4A60 aluminum/08A1 steel composite not only had corrosion resistance and met the thermal conductivity and mechanical properties, in line with the requirements of the material of the base pipe. However, under high brazing temperature and heat exchanging condition, the interfaces of composite materials were easy to form the brittle intermetallic compounds (IMC). The existence of intermetallic compounds could greatly damage the metallurgical bonding between the matrix and lead to aluminum steel layer, which affected the thermal conductivity and corrosion resistance of the materials. In this paper,4343 aluminum/4A60 aluminum/08A1 steel composite was prepared by cold rolling bonding method, Therefore, it had great significance to study the process and properties of 4343 aluminum/4A60 aluminum/08A1 steel three-layer composite materials prepared by cold rolling bonding.The cold rolling bonging process of a laminar metal composite of three steps:Surface treatment--Cold rolling bonding--Diffusion annealing. In this paper,4343 aluminum/4A60 aluminum/08A1 steel composite as the research materials. The paper investigated the effects of different process parameters for composite materials in the above mentioned three stages by various experimental instruments, such as Laser scanning confocal microscope、Universal electronic tensile machine、Nano-indenter、Optics microscope (OM)、 Scanning Electron Microscope (SEM)、Energy spectrum analyzer (EDS)、X-ray Diffraction (XRD) and so on. The specific research contents and research results are as follows:(1)Surface treatment stageAn experimental equipment, used for removing the surface’s contamination layer, was optimized and simplified the structure, and a grinding tool was designed for it. The advantages fore-mentioned were more portability and stability than before. Meanwhile, the new structure expanded the variety of parameters applied in different grinding process. Compared the different parameters of steel surface which were used wire brushing and belt grinding on steel surface morphology, surface roughness (Sa), Nano-indentation and the interface bonding strength of tri-composite metal sheet. It was indicated that belt grinding was better than wire brushing for obtaining high bonding strength under the same conditions.(2)Cold rolling bonding(CRB) stageThree aspects were investigated in this stage. Relationship between reduction and bonding strength and deformation law and mechanism in cold rolling bonding stage was researched. Some results were presented that the minimum reduction (threshold reduction) of this tri-composite metal sheet was 15%,which the stable reduction was reached to 50%.At the range of 45%～60%,the thickness and hardness of the metal tended to be stability, and a phenomenon of co-deformation were achieved, which facilitated to obtain the uniform characteristics and performance. Al/Al/Steel cold rolling bonding stage was to meet the three phase theory and thin film theory.(3)Annealing treatment stageThe diffusion mechanism and the influences among annealing process (including annealing temperature and time) and growth behavior of Intermetallic Compounds (IMC) at Al/St interface were researched. The main components of Intermetallic Compounds were identified. A conclusion was described as follow:The observation was greatly agreed with the diffusion mechanism. Some elements were diffused into the opposite side which was closed to the interface during the annealing stage. Also, the interface bonding strength improved due to the metallurgy bonding instead of mechanical bonding. The results showed that the IMC consisted of FeAl3, Fe2Al5 and FeAl, which started to formation when the temperature was approximately 580℃～590℃,and the relationship between the thickness of IMC and annealing temperature or time. |
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